The present invention relates to a delivery system in which a catheter carries a stent on its distal end portion. The stent is held in place around the catheter prior to and during percutaneous delivery by means of one and preferably two sleeves. The stent may be self-expanding, such as a NITINOL shape memory stent, or it may be expandable by means of an inflatable portion of the catheter, such as a balloon. The sleeve or sleeves have a plurality of holes which may be bored partially or completely through the material of the sleeve or sleeves. The holes may be mechanically bored or laser bored. The holes are distributed about the surface of the sleeve or sleeves in a uniform pattern but may have a variety of shapes and sizes. The sleeve or sleeves may be composed of an elastic polymer, a non-elastic polymer or a combination thereof.
Stents and stent delivery assemblies are utilized in a number of medical procedures and situations, and as such their structure and function are well known. A stent is a generally cylindrical prosthesis introduced via a catheter into a lumen of a body vessel in a configuration having a generally reduced diameter and then expanded to the diameter of the vessel. In its expanded configuration, the stent supports and reinforces the vessel walls while maintaining the vessel in an open, unobstructed condition.
Both self-expanding and inflation expandable stents are well known and widely available in a variety of designs and configurations. Self-expanding stents must be maintained under a contained sheath or sleeve(s) in order to maintain their reduced diameter configuration during delivery of the stent to its deployment site. Inflation expandable stents are crimped to their reduced diameter about the delivery catheter, then maneuvered to the deployment site and expanded to the vessel diameter by fluid inflation of a balloon positioned between the stent and the delivery catheter. The present invention is particularly concerned with delivery and deployment of inflation expandable stents, although it is generally applicable to self-expanding stents when used with balloon catheters.
In advancing an inflation expandable stent through a body vessel to the deployment site, there are a number of important considerations. The stent must be able to securely maintain its axial position on the delivery catheter without translocating proximally or distally and especially without becoming separated from the catheter. The stent, particularly its distal and proximal ends, must be protected to prevent distortion of the stent and to prevent abrasion and/or reduce trauma of the vessel walls.
Inflation expandable stent delivery and deployment assemblies are known which utilize restraining means that overlie the stent during delivery. U.S. Pat. No. 4,950,227 to Savin et al., relates to an inflation expandable stent delivery system in which a sleeve overlaps the distal or proximal margin (or both) of the stent during delivery. During inflation of the stent at the deployment site, the stent margins are freed of the protective sleeve(s). U.S. Pat. No. 5,403,341 to Solar, relates to a stent delivery and deployment assembly which uses retaining sheaths positioned about opposite ends of the compressed stent. The retaining sheaths of Solar are adapted to tear under pressure as the stent is radially expanded, thus releasing the stent from engagement with the sheaths. U.S. Pat. No. 5,108,416 to Ryan et al., describes a stent introducer system which uses one or two flexible end caps and an annular socket surrounding the balloon to position the stent during introduction to the deployment site. The entire contents of each of the patents cited herein is hereby incorporated by reference.
This invention provides an improvement over the prior art, by providing a stent delivery system wherein the stent retaining sleeves have a reduced radial and columnar strength thereby allowing a delivery catheter to deploy a balloon expandable stent at lower pressures with greater consistency than otherwise would be possible. The lower strength of the sleeves also allows the sleeves to be readily retracted from the stent without additional lubrication, however lubricants may still be applied to a stent delivery catheter using the sleeves described.